Abstract
Climate change models predict temporal and spatial shifts in precipitation resulting in more frequent incidents of flooding, particularly in regions with poor soil drainage. In these flooding conditions, crop losses are inevitable due to exposure of plants to hypoxia and the spread of root rot diseases. Improving the tolerance of bean cultivars to flooding is crucial to minimize crop losses. In this experiment, we evaluated the phenotypic responses of 277 genotypes from the Andean Diversity Panel to flooding at germination and seedling stages. A randomized complete block design, with a split plot arrangement, was employed for phenotyping germination rate, total weight, shoot weight, root weight, hypocotyl length, SPAD index, adventitious root rate, and survival score. A subset of genotypes (n = 20) were further evaluated under field conditions to assess correlations between field and greenhouse data and to identify the most tolerant genotypes. A genome-wide association study (GWAS) was performed using ~203 K SNP markers to understand the genetic architecture of flooding tolerance in this panel. Survival scores between field and greenhouse data were significantly correlated (r = 0.55, P = 0.01). Subsequently, a subset of the most tolerant and susceptible genotypes were evaluated under pathogenic Pythium spp. pressure. This experiment revealed a potential link between flooding tolerance and Pythium spp. resistance. Several tolerant genotypes were identified that could be used as donor parents in breeding pipelines, especially ADP-429 and ADP-604. Based on the population structure analysis, a subpopulation consisting of 20 genotypes from the Middle American gene pool was detected that also possessed the highest root weight, hypocotyl length, and adventitious root development under flooding conditions. Genomic regions associated with flooding tolerance were identified including a region on Pv08/3.2 Mb, which is associated with germination rate and resides in vicinity of SnRK1.1, a central gene involved in response of plants to hypoxia. Furthermore, a QTL at Pv07/4.7 Mb was detected that controls survival score of seedlings under flooding conditions. The association of these QTL with the survivability traits including germination rate and survival score, indicates that these loci can be used in marker-assisted selection breeding to improve flooding tolerance in the Andean germplasm.
Highlights
Flooding adversely affects plants by reducing ATP synthesis that is accompanied by carbohydrate starvation
Lower survivability of Andean beans can be the direct result of root rot pathogens, Pythium spp. that can spread efficiently in moist soils
These QTL can be considered as Andeanspecific QTL since they were not detected in our previous study with the majority of Middle American germplasm
Summary
Flooding adversely affects plants by reducing ATP synthesis that is accompanied by carbohydrate starvation. To deal with hypoxic conditions that result from flooding, plants use either escape or quiescence strategies (Colmer and Voesenek, 2009). Carbohydrate catabolism provides the energy for critical pathways required for plant survival These strategies vary among species and are often defined by the dominant flooding regime in the environment to which a particular species has adapted. A wide diversity of responses to flooding stress have been reported in crops (Setter and Laureles, 1996; Valliyodan et al, 2016; Soltani et al, 2017) Some crops, such as lowland rice (Oryza sative L.), are well-adapted to flooding, the majority of economically important crops, including common bean, are susceptible
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